I just want to play devil's advocate for a moment; You say this nonchalantly, but that's the most important bit of your statement. If one of those two roommates were under investigation or were on some watch-list (for a valid reason or not), you should fully expect the FBI to keep tabs on those who they were living with. That would include you. Now whether they were watching your ex-roommates for a good reason is neither here nor there, but the fact remains that the FBI wouldn't be doing their jobs if they didn't keep tabs on you, someone whom they were living with.